Apparatus and method for purifying cumene

ABSTRACT

The present application relates to an apparatus and method for purifying cumene. The apparatus and method for purifying cumene according to the present application can reduce the amount of energy consumption which occurs during purification processes and can provide an apparatus and method capable of efficiently purifying cumene.

TECHNICAL FIELD

The present application relates to an apparatus and method for purifyingcumene.

Specifically, the present application relates to an apparatus and methodfor purifying cumene to increase the energy efficiency in thepurification process.

BACKGROUND ART

Cumene is isopropylbenzene (C₆H₅CH(CH₃)₂), and it is used as animportant intermediate material in a variety of chemical industries,polymer industries, etc. At present, most of the cumene(isopropylbenzene) being produced is used for the preparation of phenol,acetone, etc.

Cumene is generally produced by reacting benzene and propylene underliquid or gas phase conditions in the presence of a catalyst.Technologies related to the preparation of cumene are proposed in KoreanUnexamined Patent Application Publication No. 10-2011-0082160 and KoreanUnexamined Patent Application Publication No. 10-2013-0008595, etc.

Cumene is mostly commercially prepared through an alkylation reactionand a trans alkylation reaction. Accordingly, an apparatus for preparingcumene includes an alkylation reaction unit and a trans alkylationreaction unit.

In the alkylation reaction unit, benzene and propylene react to producecumene (isopropylbenzene) and, as a by-product, polyisopropylbenzenes(PIPB) such as diisopropylbenzene (DIPB), triisopropylbenzene (TIPB),etc. are produced through a reaction between cumene and propylene. Thecompetitive reaction in the preparation of cumene is a polyalkylationreaction. In other words, it is a side reaction which produces theabove-described PIPBs such as DIPB, TIPB, etc.

The trans alkylation reaction unit is used to react polyalkylatedbenzene, which is the PIPB, etc. produced through the above-describedside reaction, with benzene to produce additional cumene.

Also, in addition to the substances described above, light materials(lights) such as C3 (propylene, propane, etc.), etc. and heavy materials(heavies), which are heavier than PIPB, are produced as additionalproducts during the preparation of cumene, and along with thesematerials, unconsumed benzene, water, etc. are present. Therefore, inthe alkylation reaction unit and trans alkylation reaction unit, lightssuch as C3 (propylene, propane, etc.), etc., PIPB, unconsumed benzene,water and other heavies, etc. are discharged in addition to the cumene(isopropylbenzene) of interest; these materials are either removed orrecycled through a purification process in pursuit of high puritycumene.

In general, three distillation columns are used in the purificationprocess of cumene. FIG. 1 is a diagram illustrating the configuration ofan apparatus for purifying cumene according to the prior art. Referringto FIG. 1, the purification process for cumene according to the priorart can be schematically illustrated as follows.

The apparatus for purifying cumene is generally installed in connectionwith the above-described alkylation reaction unit and trans alkylationreaction unit, and includes 3 distillation columns such as a firstdistillation column, a second distillation column and a thirddistillation column.

The first distillation column is a benzene column 1 which recoversbenzene from streams from the alkylation reaction unit and transalkylation reaction unit.

In this case, an in-put line 1 b which takes in a stream discharged fromthe alkylation reaction unit and an in-put line 1 c which takes in astream discharged from the trans alkylation reaction unit are connectedto the front end portion of the benzene column 1. Also, an in-put linela through which fresh benzene flows in is connected to the front endportion of the benzene column 1. In addition, lights such as C3, etc.and water are discharged from the upper portion of the benzene column 1through a lights out-put line 1 d, whereas a cumene stream is dischargedfrom the lower portion through a cumene stream out-put line 1 e.Further, benzene is discharged from substantially the center of thebenzene column 1 through a benzene recycle line 1 f, and the dischargedbenzene is recycled.

The second distillation column is a cumene column 2 which recoverscumene from the cumene stream discharged from the lower portion of thebenzene column 1.

In this case, cumene is discharged from the upper portion of the cumenecolumn 2 through a cumene out-put line 2 a and recovered. Also, from thelower portion of the cumene column 2, a PIPB stream is dischargedthrough a PIPB out-put line 2 b.

The third distillation column is a PIPB column 3 which takes in andrecycles the PIPB stream discharged from the lower portion of the cumenecolumn 2.

In this case, PIPBs such as DIPB, etc. are discharged from the upperportion of the PIPB column 3 through a PIPB out-put line 3 a andrecycled. Also, from the lower portion of the PIPB column 3, heavies aredischarged through a heavies out-put line 3 b.

Cumene (isopropylbenzene) of interest can be purified to a high purityand recovered through a purification process such as the above. Inaddition, energy is consumed in the above-described purificationprocess. To each of the columns 1, 2 and 3, a heat source is providedfor the separation of substances by the differences in boiling points,and most of the energy is consumed in such a separation process. In FIG.1, reference numeral C represents a condenser, and reference numeral Brepresents a heat exchanger (or reboiler) for supplying heat.

However, the cumene purification process according to the prior artrequires a large consumption of energy. As described above, each of thecolumns 1, 2 and 3 is provided with a heat source for the separation ofsubstances, and without an efficient use of the heat sources beingreviewed, the amount of energy consumed is large especially in such aseparation process.

DISCLOSURE Technical Problem

The present application provides an improved apparatus and method forpurifying cumene.

With the apparatus and method for purifying cumene according to thepresent application, excellent energy efficiency can be achieved.

Technical Solution

The present application is devised to solve the aforementioned problems,and relates to an apparatus for purifying cumene including:

a lights cut column which takes in a stream from an alkylation reactionunit and discharges lights and water from the upper portion;

a benzene column which takes in a stream from a trans alkylationreaction unit and the stream discharged through the lower portion of thelights cut column to separate them into benzene and a cumene stream;

a cumene column which takes in the cumene stream from the benzene columnto separate it into cumene and a polyisopropylbenzene (PIPB) stream;

a PIPB column which takes in the PIPB stream from the cumene column toseparate it into PIPB and heavies;

a temperature dropping unit which reduces the temperature at the lowerportion of the benzene column; and

a cumene out-put line which is installed at the upper portion of thecumene column.

In the apparatus for purifying cumene according to the presentapplication, the cumene out-put line may be connected to a heatexchanger of the benzene column to supply heat to the lower portion ofthe benzene column.

In one example, the benzene column and cumene column may operate in theways to satisfy Mathematical Formula 1 below.

T₃-T₂≥10° C.   [Mathematical Formula 1]

(In the Mathematical Formula 1 above, T₂ represents the temperature atthe lower portion of the benzene column, whereas T₃ represents thetemperature at the upper portion of the cumene column).

In one example, the PIPB column may include a PIPB out-put lineinstalled at the upper portion, and the PIPB out-put line may beconnected to one or more heat exchangers selected among a heat exchangerof the benzene column and a heat exchanger of the cumene column.

In addition, the present application may relate to a method forpurifying cumene, where the method includes:

a lights removal process in which a stream from the alkylation reactionunit is introduced into the lights cut column and removed of lights andwater;

a benzene separation process in which a stream from the trans alkylationreaction unit and the stream discharged through the lower portion of thelights cut column are introduced into the benzene column and separatedinto benzene and a cumene stream;

a cumene separation process in which the cumene stream separated earlieris introduced into the cumene column and separated into cumene and aPIPB stream; and

a PIPB separation process in which the PIPB stream separated earlier isintroduced into the PIPB column and separated into PIPB and heavies.

In one example, the method for purifying cumene according to the presentapplication may further include a process in which the cumene dischargedat the upper portion of the cumene column passes through the heatexchanger of the benzene column.

In one example, the method for purifying cumene according to the presentapplication may have the temperature at the lower portion of the benzenecolumn maintained in the range of 130° C. to 200° C.

In one example, the method for purifying cumene according to the presentapplication may have the temperature at the upper portion of the cumenecolumn maintained in the range of 140° C. to 210° C.

In one example, the method for purifying cumene according to the presentapplication may be operated in the way that the benzene column andcumene column satisfy Mathematical Formula 1 below.

T₃-T₂≥10° C.   [Mathematical Formula 1]

(In the Mathematical Formula 1 above, T₂ represents the temperature atthe lower portion of the benzene column, whereas T₃ represents thetemperature at the upper portion of the cumene column).

In one example, the method for purifying cumene according to the presentapplication may have the pressure in the benzene column maintained inthe range of 10 to 230 kPa.

Advantageous Effects

According to the present application, the purification process isimproved so that the energy efficiency can increase. Specifically,according to the present application, the vapor heat source of thecumene column is used as the heat source for the benzene column, andtherefore, the amount of energy consumed can be effectively reduced.

DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram illustrating the configuration of an apparatus forpurifying cumene according to the prior art.

FIG. 2 is a diagram illustrating the configuration of an apparatus forpurifying cumene according to the first embodiment of the presentapplication.

FIG. 3 is a diagram illustrating the configuration of an apparatus forpurifying cumene according to the second embodiment of the presentapplication.

FIG. 4 is a diagram illustrating the configuration of an apparatus forpurifying cumene applied in a comparative example.

FIG. 5 is a diagram illustrating the configuration of an apparatus forpurifying cumene applied in an example.

DESCRIPTION OF REFERENCE NUMERALS

10: benzene column

12 : in-put line for stream from trans alkylation reaction unit

14 : benzene recycle line

15 : temperature dropping unit

16 : cumene stream out-put line

20 : cumene column

25 : cumene out-put line

26 : polyisopropylbenzene (PIPB) stream out-put line

30 : PIPB column

34 : PIPB out-put line

36 : heavies out-put line

40 : lights cut column

41 : benzene in-put line

42 : in-put line for stream from alkylation reaction unit

44 : upper stream out-put line

46 : lower stream out-put line

MODES FOR INVENTION

Hereinafter, the apparatus and method for purifying cumene according tothe present application will be described in more detail with referenceto the accompanying drawings and an example.

In the present specification, “and/or” is used to indicate that one ormore of the components listed before or after are included.

In the present specification, “connection”, “installation”,“combination”, etc. refer to the two members which can be engaged withor disengaged from each other, as well as to an integral structure.Specifically, the terms such as “connection”, “installation”,“combination”, etc. describe, for example, two members which areconfigured to be engaged with or disengaged from each other through aforce-fit manner, a fitting manner using grooves and projections, acoupling manner using coupling members such as screws, bolts, pieces,rivets, brackets, etc., as well as an integral body of two members whichbecome inseparable once combined through welding, an adhesive, anintegral molding or the like.

The terms such as “first”, “second”, “third”, “one end”, “the otherend”, etc. in the present specification are used to distinguish oneelement from the other, and it should be understood that each of thecomponents is not limited by the above-described terms. Hereinafter, inthe description of the present application, detailed descriptions of anyrelated generic functions or configurations well-known in the art willbe omitted.

In the present application, an “A stream” refers to a stream whichincludes at least an ‘A’ component, and it may include the ‘A’ componentas a main component. For example, a “polyisopropylbenzene (PIPB) stream”is a stream which includes at least ‘PIPB’, and it may include ‘PIPB’ asa main component.

Meanwhile, the above-described ‘including PIPB as a main component’ maymean that PIPB is included the most among various components of thestream.

In the present application, an “A/B stream” refers to a stream whichincludes at least an ‘A’ component and a ‘B’ component, and an “A/B/Cstream” refers to a stream which includes at least an ‘A’ component, an‘B’ component and a ‘C’ component. For example, “benzene/cumene/PIPBstream” may refer to a stream which includes at least ‘benzene’,‘cumene’ and ‘PIPB’.

In the present application, an “A column” refers to a column whichseparates at least an ‘A’ substance from an inflow. For example, “abenzene column 10” is a column which separates at least ‘benzene’, and“a cumene column 20” is a column which separates at least ‘cumene’.Also, “a PIPB column 30” is a column which separates at least ‘PIPB’.

The present application relates to an apparatus for purifying cumene.The apparatus for purifying cumene according to the present applicationmay be installed in connection with, for example, a preparationapparatus of cumene.

In one example, the apparatus for purifying cumene according to thepresent application may be installed in connection with the alkylationreaction unit and trans alkylation reaction unit which constitute thepreparation apparatus of cumene.

As described earlier, in the above-described alkylation reaction unit,benzene and propylene react to produce PIPBs such as DIPB, TIPB, etc.

In this case, the produced cumene is separated and recovered through arecovery line, and the stream including the above-described by-productis discharged through a separate line.

In addition to the above-described PIPB as a by-product, lights such asC3 (propylene, propane, etc.), etc., unrecovered cumene in a smallamount, unconsumed benzene, water, other high-weight heavies, etc. arepresent in the stream discharged from the above-described alkylationreaction unit.

In addition, in the above-described trans alkylation reaction unit,polyalkylated benzene, which is the PIPB produced through theabove-described side reaction, reacts with benzene to produce additionalcumene. In the stream discharged from the above-described transalkylation reaction unit, heavies which are heavier than PIPB arepresent in addition to PIPB.

The apparatus for purifying cumene according to the present applicationcan take in a stream from the alkylation reaction unit and a stream fromthe trans alkylation reaction unit, and purify them as described above.In this case, there is no particular limitation to the above-describedstreams, as long as they are discharged from the alkylation reactionunit and trans alkylation reaction unit. For example, the streamdischarged from the above-described alkylation reaction unit may be aby-product stream from which cumene is removed (recovered) byseparation, or in some cases, it may be a cumene stream which isseparated through a cumene recovery line.

Specifically, the apparatus for purifying cumene according to thepresent application may take in a stream from the alkylation reactionunit and a stream from the trans alkylation reaction unit separatelythrough distillation columns, which are different from each other.

In one example, the apparatus for purifying cumene according to thepresent application includes, as exemplified in FIG. 2, a lights cutcolumn 40 which is installed in front of a benzene column 10; thebenzene column 10 which takes in a lower stream from the lights cutcolumn 40 and separates it into benzene and a cumene stream; a cumenecolumn 20 which takes in the cumene stream from the benzene column 10and separates it into cumene and a PIPB stream; a PIPB column 30 whichtakes in the PIPB stream from the cumene column 20 and separates it intoPIPB and heavies; a temperature dropping unit 15 which reduces thetemperature at the lower portion of the benzene column 10; and a cumeneout-put line 25 which is installed at the upper portion of the cumenecolumn 20. In this case, the cumene out-put line 25 may be connected toa heat exchanger B of the benzene column 10 to supply heat to the lowerportion of the benzene column 10.

In a specific example, the lights cut column 40 can take in a streamfrom the alkylation reaction unit to remove lights and water bydischarging them from the upper portion.

In a specific example, the benzene column 10 can serve to take in astream discharged from the lower portion of the lights cut column 40 anda stream from the trans alkylation reaction unit to separate them intobenzene and a cumene stream.

In a specific example, the cumene column 20 can serve to take in thecumene stream from the benzene column 10 to separate it into cumene anda PIPB stream.

In a specific example, the PIPB column 30 can serve to take in the PIPBstream from the cumene column 20 to separate it into PIPB and heavies.

Hereinafter, the apparatus for purifying cumene according to the presentapplication will be described in more detail with reference toaccompanying drawings.

FIG. 2 is an exemplifying diagram of the apparatus for purifying cumeneaccording to the present application.

Referring to FIG. 2, the apparatus for purifying cumene according to thepresent application includes a benzene column 10, a cumene column 20which is installed at the back of the benzene column 10, a PIPB column30 which is installed at the back of the cumene column 20, and a lightscut column 40 which is installed in front of the benzene column 10.

In the present application, each of the columns 10, 20, 30 and 40 may beselected from the distillation columns used in distillation processes ingeneral industries.

In addition, there is no particular limitation to the operatingconditions, for example, the plate number, inner diameter, pressure,temperature, reflux ratio of the upper and lower effluents, etc. of eachof the columns 10, 20, 30 and 40 in the present application, and theymay be freely redesigned by an ordinary person skilled in the art withina range in which the objects of the present application can be achieved.

As shown in FIG. 2, a condenser and/or heat exchanger (or reboiler) maybe installed in each of the columns 10, 20, 30 and 40 of the presentapplication. In FIG. 2, reference numeral C represents a condenser,whereas reference numeral B represents a heat exchanger (or reboiler).

In this case, the condenser C and/or heat exchanger B may be installedor not installed depending on each of the columns 10, 20, 30 and 40.

In this case, the condenser C and heat exchanger B are, unless specifiedotherwise, the components which may be omitted even when illustrated ina diagram, or, conversely, they are the components which may be included(installed) even when not illustrated in a diagram.

The apparatus for purifying cumene according to the present applicationhas a structure which, compared to the conventional purificationapparatus as illustrated in FIG. 1, further includes a light cut column40. As changes are made to the influent and effluent flow linesaccordingly, a structure with improved energy efficiency can beobtained.

Specifically, the lights cut column 40 of the apparatus for purifyingcumene according to the present application can remove lights and waterby taking in a stream of the alkylation reaction unit and dischargingfrom the upper portion.

The lights cut column 40 may include at least one of in-put lines 41 and42 installed in the front end portion.

In one example, the in-put lines 41 and 42 may include an in-put line 42through which a stream discharged in the alkylation reaction unit flowsin.

In addition, in another exemplary embodiment, the in-put lines 41 and 42may further include a benzene in-put line 41 through which fresh benzeneflows in. That is, the lights cut column 40 is positioned in the frontend in the apparatus for purifying cumene according to the presentapplication, and may further include a benzene in-put line through whichfresh benzene flows in.

As illustrated in FIG. 2, the benzene in-put line 41 may be installed atsubstantially the upper portion of the lights cut column 40, and anin-put line 42 for a stream from the alkylation reaction unit may beinstalled below the benzene in-put line 41, but they are not limitedthereto.

The lights cut column 40 takes in fresh benzene and a stream from thealkylation reaction unit, and separates them into an upper stream(materials having a low boiling point) and a lower stream (materialshaving a high boiling point). The lights cut column 40 includes an upperstream out-put line 44 installed at the upper portion and a lower streamout-put line 46 installed at the lower portion.

Through the upper stream out-put line 44, lights such as C3 (propylene,propane, etc.), etc. and water are discharged to be removed. In thiscase, the above-described lights such as C3 (propylene, propane, etc.),etc. may be included mainly in a stream from the alkylation reactionunit and the above-described water may be included mainly in freshbenzene. In addition, the above-described lower stream containsmaterials with a high boiling point which are inclusive of benzene,cumene, PIPB, heavies, etc. and exclusive of lights and water. Such alower stream is discharged through the lower stream out-put line 46 andintroduced into the benzene column 10.

The benzene column 10 is installed at the back of the lights cut column40, and it may separate the introduced stream into benzene and a cumenestream.

The benzene column 10 may have an in-put line 12 for a stream from thetrans alkylation reaction unit and a lower stream out-put line 46 of thelights cut column 40 connected to its front end. Accordingly, thebenzene column 10 may take in the stream from the trans alkylationreaction unit and a stream discharged through the lower portion of thelights cut column 40 to separate them into benzene and a cumene stream.

In addition, the benzene column 10 may include a benzene recycle line 14installed at the upper portion and a cumene stream out-put line 16installed at the lower portion.

In the benzene column 10, separation into 2 phases of benzene and acumene stream is possible, and the benzene separated in the benzenecolumn 10 can be discharged through the benzene recycle line 14 andrecycled.

In this case, the benzene discharged through the benzene recycle line 14can be, for example, supplied to the alkylation reaction unit and/ortrans alkylation reaction unit and recycled, and, in some cases,recycled through the benzene in-put line 41 into the lights cut column40.

The above-described cumene stream may be discharged, for example,through the cumene stream out-put line 16 and introduced into the cumenecolumn 20.

The cumene column 20 takes in the cumene stream from the benzene column10 and separates it into cumene and a PIPB stream. The cumene column 20may include a cumene out-put line 25 installed at the upper portion anda PIPB stream out-put line 26 installed at the lower portion.

The cumene separated at the cumene column 20 may be discharged from theupper portion through the cumene out-put line 25, and the dischargedcumene may be recovered as a product.

In this case, one end of the cumene out-put line 25 is connected to theupper portion of the cumene column 20 and the other end is connected toa heat exchanger B of the benzene column 10 to provide a heat source tothe benzene column 10.

In one example, the cumene out-put line may be connected to a heatexchanger of the benzene column to supply heat to the lower portion ofthe benzene column. As above, when the cumene out-put line is connectedto the heat exchanger of the benzene column, the vapor of cumene becomesa heat source, and therefore, the energy required for supplying heat tothe lower portion of the benzene column can be reduced. More specificdetails will be described below.

In addition, the PIPB stream separated in the cumene column 20 isdischarged through the out-put line 26 and introduced into the PIPBcolumn 30.

The PIPB column 30 can take in the PIPB stream from the cumene column 20and separate it into PIPB and heavies.

In this case, according to one embodiment, the PIPB column 30 mayinclude a PIPB out-put line 34 installed at the upper portion and aheavies out-put line 36 installed at the lower portion.

The PIPB separated in the above-described PIPB column 30 is dischargedfrom the upper portion through the out-put line 34, and the dischargedPIPB may be supplied, for example, to the trans alkylation reaction unitand recycled.

The PIPB stream introduced from the cumene column 20 may contain PIPBssuch as DIPB, TIPB, etc.

In this case, for example, DIPB among the above-described DIPB and TIPBmay be separated through the PIPB column 30, discharged through theout-put line 34, supplied to the trans alkylation reaction unit andrecycled.

In addition, the PIPB column 30 may include, for example, a plurality ofPIPB out-put lines 34 which separate PIPBs by type.

Specifically, the PIPB column 30 includes a TIPB out-put line installedat a plate having substantially a median plate number and a DIPB out-putline 34 installed at the upper portion, and thus, it can separatepolyalkylation benzene by type at multiple plates.

Meanwhile, the heavies discharged through the heavies out-put line 36are the heaviest materials in the process, and may specifically refer tomaterials heavier (materials having a higher boiling point) than PIPB.

Such heavies may be discharged through the out-put line 36, cooled andthen sent to a storage tank.

The apparatus for purifying cumene according to the present applicationincludes 4 columns 10, 20, 30 and 40 as described above, and,additionally as the means to improve energy efficiency, it may include atemperature dropping unit 15 which drops a temperature T₂ at the lowerportion of the benzene column 10.

In the present application, there is no particular limitation to thetemperature dropping unit 15 as long as it can reduce the temperature T₂at the lower portion of the benzene column 10.

According to an exemplary embodiment of the present application, such adropping of temperature may be achieved by reducing the internalpressure P₁ of the benzene column 10.

For example, the temperature dropping unit 15 may include a pressuredropping means to reduce the internal pressure of the benzene column 10.

Specifically, the temperature dropping unit 15 may include a vacuum pumpas the pressure dropping means. In the drawings, a vacuum pump isillustrated as an example of the temperature dropping unit 15. However,in the present application, the temperature dropping unit 15 is notlimited to a vacuum pump, and it is not particularly limited to acertain type as long as it can reduce the temperature T₂ at the lowerportion of the benzene column 10.

In addition, there is no particular limitation to the installationposition of the temperature dropping unit 15. The temperature droppingunit 15 may be installed inside the benzene column 10, or it may beinstalled in a way so that it is positioned outside the benzene column10 and connected to the benzene column 10.

The temperature dropping unit (e.g. a vacuum pump is used) 15 may beinstalled in a way so that it is connected to a side wall of the benzenecolumn 10.

In this case, the vacuum pump may be connected and installed as close aspossible to the side wall of the benzene column 10, so that it canresult in a maximum ability to reduce pressure (suction strength).

In dropping of the temperature T₂ at the lower portion of the benzenecolumn 10, the temperature T₂ at the lower portion should be maintainedhigher than the temperature T₁ at the upper portion so as not toadversely affect the separation efficiency of the benzene column 10.

In other words, T₂ should be maintained higher than T₁ as illustrated inFIG. 2. In consideration of this point, it may be preferable that thetemperature T₂ at the lower portion is reduced as a result of a reducedinternal pressure P₁ as exemplified above.

Specifically, when the internal pressure P₁ is reduced, the temperatureT₁ at the upper portion and temperature T₂ at the lower portion drop ineven proportions, and therefore, T₂>T₁ can be maintained with a simpleoperation.

The apparatus for purifying cumene according to the present applicationincludes a cumene out-put line installed at the upper portion of thecumene column. The cumene out-put line 25 may be connected to a heatexchanger B of the benzene column 10 to supply heat to the lower portionof the benzene column 10.

Specifically, a heat exchanger B is installed at the lower portion ofthe benzene column 10, and the cumene out-put line 25 may be connectedto such a heat exchanger B. In other words, one end of the cumeneout-put line 25 may be connected to the upper portion of the cumenecolumn 20, whereas the other end may be connected to the heat exchangerB of the benzene column 10.

More specifically, when the purification apparatus is designed asdescribed above, it may be able to supply heat to the lower portion ofthe benzene column 10 by reducing the temperature T₂ at the lowerportion of the benzene column 10 and passing the cumene, which isdischarged from the upper portion of the cumene column 20, through theheat exchanger B of the benzene column 10 prior to recovery. Inaddition, the cumene which passed through the heat exchanger B may berecovered as a product.

Therefore, according to the present application, the vapor heat sourceof the cumene discharged from the cumene column 20 may be used as areplacement for the source of heat supplied to the lower portion of thebenzene column 10. Therefore, the energy required for supplying heat tothe lower portion of the benzene column 10 can be reduced.

In addition, the temperature T₂ at the lower portion of the benzenecolumn 10 has been reduced earlier as described above, and therefore,the heat required for the separation process in the benzene column 10can be sufficiently provided by the vapor heat source of cumene alone,and this may be efficient in recycling heat energy.

In one example, the benzene column 10 and cumene column 20 may beoperated in the way that Mathematical Formula 1 below is satisfied.

T₃-T₂>10° C.   [Mathematical Formula 1]

In the Mathematical Formula above, T₂ represents the temperature at thelower portion on the inside of the benzene column 10, whereas T₃represents the temperature at the upper portion of the inside of thecumene column 20.

In other words, operations may be performed in the way that thetemperature T₃ at the upper portion of the inside of the cumene column20 is maintained higher than the temperature T₂ at the lower portion ofthe inside of the benzene column 10 by 10° C. or more.

When the Mathematical Formula 1 above is satisfied, it may be highlybeneficial in terms of energy efficiency. That is, when the MathematicalFormula 1 above is satisfied, the amount of energy consumed can beeffectively reduced.

Considering this point, it may be preferable to have the temperature T₃at the upper portion of the cumene column 20 maintained higher than thetemperature T₂ at the lower portion of the benzene column 10 by 15° C.or more (T₃-T₂>15° C.), or 20° C. or more (T₃-T₂>20° C.), by reducingthe temperature T₂ at the lower portion.

In this case, there is no particular upper limit to the differencebetween the two temperatures, but it may be, for example, 80° C. or 60°C. In other words, T₃-T₂>80° C. or T₃-T₂>60° C. may be satisfied.

In one example, the temperature T₃ at the upper portion of the cumenecolumn 20 may be 140° C. or more, and specifically, it may be in therange of 140° C. to 210° C.

The temperature T₂ at the lower portion of the benzene column 10 may be,for example, in the range of 200° C. or less, and specifically, 130° C.to 200° C., through a dropping of the internal pressure P₁.

In addition, the internal pressure P₁ of the benzene column 10 may bebeneficial to the process when maintained at a low level.

The internal pressure P₁ of the benzene column 10 can have, for example,the temperature T₂ at the lower portion maintained within theabove-described range, through a pressure dropping.

Specifically, the internal pressure P₁ of the benzene column 10 may bemaintained at the level of, for example, 500 kPa or less, 300 kPa orless, or 230 kPa or less. At the same time, the lower limit of theinternal pressure P₁ of the benzene column 10 may be 5 kPa or more, or10 kPa or more, but it is not particularly limited thereto. The internalpressure P₁ of the benzene column 10 may be adjusted to fall within therange of, for example, 5 kPa to 300 kPa, 5 kPa to 300 kPa, 10 kPa to 300kPa, or 10 kPa to 230 kPa.

Meanwhile, in the present application, the separation of cumene in thecumene column 20 may include the case where all of the cumene passesthrough the heat exchanger B of the benzene column 10 and the case wherea part of the cumene passes through the heat exchanger B of the benzenecolumn 10.

Specifically, the cumene separated in the cumene column 20 may besupplied in its entirety through the cumene out-put line 25 to the heatexchanger B of the benzene column 10. In addition, the cumene separatedin the cumene column 20 is discharged through two lines 25 and 25′; apart of it may be supplied through a first cumene out-put line 25 to theheat exchanger B of the benzene column 10, while the rest beingdischarged through a second cumene recovery line 25′.

In this case, the cumene discharged through the second cumene recoveryline 25′ is cooled and then collected in a storage tank. At the sametime, the cumene which is supplied through the first cumene out-put line25 to the heat exchanger B of the benzene column 10 may be cooled afterproviding heat to the benzene column 10 and then collected in a storagetank.

In addition, according to an exemplary embodiment, the cumene out-putline 25 may be heat-insulated.

Specifically, the cumene out-put line 25 may have a covering of athermal insulation material or heating means such as hot wires on thesurface so that it can avoid heat loss during the course of cumenetransport through the cumene out-put line 25 to the heat exchanger B ofthe benzene column 10.

With the apparatus for purifying cumene according to the presentapplication, lights and water are removed in advance by the lights cutcolumn 40 before they are introduced into the benzene column 10;therefore, an adverse effect which may result from a temperaturedropping of the benzene column 10 can be prevented, and at the sametime, a purification process in the benzene column 10 can be improvedand energy efficiency can be ultimately enhanced.

Specifically, when it is intended to remove lights such as C3(propylene, propane, etc.), etc. (included in alkylation reactants) andwater (included in fresh benzene) from the benzene column 10 in aconventional way of discharging them from the upper portion withoutrequiring installation of the lights cut column 40, a temperaturedropping of the benzene column 10 may cause much stress to the condenserC.

More specifically, in the reduction of the temperature T₂ at the lowerportion of the benzene column 10, to reduce the internal pressure P₁ ofthe benzene column 10 as described earlier may be considered as apreferable option. In this case, when the internal pressure P₁ of thebenzene column 10 drops, the temperature T₁ at the upper portion as wellas the temperature T₂ at the lower portion decreases. In this case, thetemperature T₁ at the upper portion may decrease below zero due to anexcessive reduction in the internal pressure P₁, causing much stress tothe condenser C.

However, the apparatus for purifying cumene according to the presentapplication has a lights cut column 40 installed in front of the benzenecolumn 10 as described above; in this way, it can remove lights inalkylation reactants and water (moisture) in fresh benzene through thelights cut column 40 in advance, thereby preventing the above-describedphenomenon and enabling a temperature dropping through the reduction ofpressure P₁ of the benzene column 10. In addition, from the upperportion of the benzene column 10, substantially pure benzene can beseparated.

In addition, according to the prior art, lights and water (from theupper portion of a benzene column 1), benzene (from the central portionof the benzene column 1) and a cumene stream (from the upper portion ofthe benzene column 1) are separately discharged from the apparatus forpurifying cumene as seen in FIG. 1. In this case, sectioning is requiredto accommodate the 3 phases, and therefore, operating conditions (platenumber, pressure, temperature, etc.) of the benzene column 1 may bedifficult to deal with, and the separation efficiency of benzene maydegrade. In other words, it may be difficult to separate benzene with ahigh purity.

In contrast, with the apparatus for purifying cumene according toembodiments of the present application, lights and water are removed bythe lights cut column 40 in advance as shown in FIG. 2. Therefore, aseparation process into 2 phases of benzene and a cumene stream takesplace in the benzene column 10, and, accordingly, setting up theoperation conditions for the upper portion and lower portion may be madeeasier. In addition, with only the operation conditions for benzene(pressure, temperature, etc.) being considered, high purity benzene canbe obtained by separation at a high efficiency.

Moreover, with the apparatus for purifying cumene according to thepresent application, the purification process can be further improved byconnecting the in-put line 42 for a stream from the alkylation reactionunit to the lights cut column 40, and connecting the in-put line 12 fora stream from the trans alkylation reaction unit to the benzene column10 as described earlier.

For example, connecting both stream in-put lines 12 and 42 to the lightscut column 40 may be taken into consideration; but in this case, a loadmay be exerted on the lights cut column 40, thus reducing efficiency inthe separation process in the lights cut column 40 itself and,furthermore, in carrying out the overall purification processcontinuously.

However, in the apparatus for purifying cumene according to the presentapplication, each of 2 streams is separately introduced into the lightscut column 40 and benzene column 10, respectively, thereby reducing theload on each of columns 10 and 40 and enabling a continuous purificationprocess with high efficiency.

Also, the apparatus for purifying cumene according to the presentapplication can supply heat to the lower portion of any one or both ofthe benzene column 10 and cumene column 20 by passing the PIPBdischarged at the upper portion of the PIPB column 30 through one ormore heat exchangers B selected among the heat exchanger B of thebenzene column 10 and heat exchanger B of the cumene column 20.

Specifically, the PIPB out-put line 34 may be connected to one or moreheat exchangers B selected among the heat exchanger B of the benzenecolumn 10 and heat exchanger B of the cumene column 20. Accordingly, thevapor heat source of PIPB may be recycled as the heat source of thebenzene column 10 and/or of the cumene column 20, and thus, energyefficiency can increase.

More specifically, as illustrated in FIG. 3, the PIPB out-put line 34may be connected, for example, to the heat exchanger B of the benzenecolumn 10. In addition, the PIPB which passed through a heat exchanger Bmay be supplied to the trans alkylation reaction unit after supplyingheat to be recycled.

The present application is also related to a method for purifying cumeneusing the above-described apparatus. The method for purifying cumeneaccording to the present application may be carried out by using theabove-described lights cut column, benzene column, cumene column andPIPB column.

For example, the method for purifying cumene according to the presentapplication includes:

a lights removal process in which a stream from the alkylation reactionunit is introduced into the lights cut column and removed of lights andwater;

a benzene separation process in which a stream from the trans alkylationreaction unit and the stream discharged through the lower portion of thelights cut column are introduced into the benzene column and separatedinto benzene and a cumene stream;

a cumene separation process in which the cumene stream separated earlieris introduced into the cumene column and separated into cumene and aPIPB stream; and

a PIPB separation process in which the PIPB stream separated earlier isintroduced into the PIPB column and separated into PIPB and heavies.

The above-described lights removal process may be carried out in thelights cut column 40. A stream from the alkylation reaction unit isintroduced into the lights cut column 40, and, for example, lights andwater may be removed through the upper portion, and materials having ahigh boiling point, specifically, benzene, cumene, PIPB, heavies, etc.may be separated through the lower portion.

Also, the lights removal process may further include a step of taking inbenzene through the benzene in-put line installed at the front endportion.

The above-described benzene separation process may be carried out in thebenzene column 10, and it may include a step of taking in a stream fromthe trans alkylation reaction unit and a stream discharged at the lowerportion of the lights cut column to separate, for example, benzenethrough the upper portion and a cumene stream through the lower portion.

The benzene separated through the upper portion may be supplied througha benzene recycle line to, for example, the alkylation reaction unitand/or trans alkylation reaction unit and recycled, and in some cases,it may be recycled through the benzene in-put line 41 to the lights cutcolumn 40.

The above-described benzene column may include a temperature droppingunit 15 which drops the temperature T₂ at the lower portion, and it maybe possible that the decrease in the temperature of the benzene columnis induced from the reduction of the internal pressure of the benzenecolumn.

In other words, the method for purifying cumene according to the presentapplication can induce dropping of the internal pressure of the benzenecolumn, ultimately reducing the temperature at the lower portion of thebenzene column, by further including a lights removal process prior tothe benzene separation process.

In addition, as the temperature at the lower portion of the benzenecolumn drops, the vapor heat source of cumene, which may be obtained bypassing the cumene discharged at the upper portion of the cumene columnthrough the heat exchanger of the benzene column, can single-handedlysupply enough heat required for the separation process of the benzenecolumn 10, ultimately leading to energy savings.

In one example, the method for purifying cumene according to the presentapplication may include having the internal pressure of the benzenecolumn maintained in the range of 10 kPa to 230 kPa. In addition, it mayinclude having the temperature at the lower portion of the benzenecolumn maintained in the range of 130° C. to 200° C.

The above-described cumene separation process may be carried out in thecumene column 20, and it may include steps of taking in a cumene streamand separating, for example, cumene through the upper portion and a PIPBstream through the lower portion.

The cumene separated through the upper portion earlier may be passedthrough, for example, the heat exchanger of the benzene column.

In other words, the method for purifying cumene according to the presentapplication may further include a step of passing the cumene dischargedfrom the upper portion of the cumene column through the heat exchangerof the benzene column. When the cumene separated from the cumene columnis passed through the heat exchanger of the benzene column as describedabove, the cumene vapor becomes the heat source, and thus, the energy ofthe heat exchanger installed in the benzene column can be reduced.

In one example, the method for purifying cumene according to the presentapplication may include having the temperature at the upper portion ofthe cumene column maintained in the range of 140° C. to 210° C.

In addition, the method for purifying cumene according to the presentapplication may include operating the benzene column 10 and cumenecolumn 20 in a way so that Mathematical Formula 1 below is satisfied.

T₃-T₂>10° C. [Mathematical Formula 1]

In the Mathematical Formula above, T₂ represents the temperature at thelower portion of the inside of the benzene column 10, whereas T₃represents the temperature at the upper portion of the inside of thecumene column 20.

In other words, operations may be performed in a way so that thetemperature T₃ at the upper portion of the inside of the cumene column20 is maintained higher than the temperature T₂ at the lower portion ofthe inside of the benzene column 10 by 10° C. or more.

When the Mathematical Formula 1 above is satisfied, it may be highlybeneficial in terms of energy efficiency. That is, when MathematicalFormula 1 above is satisfied, the amount of energy consumed can beeffectively reduced.

Also, the method for purifying cumene according to the presentapplication may further include a step of passing the PIPB dischargedfrom the upper portion of the PIPB column through one or more heatexchangers selected among the heat exchanger of the benzene column andheat exchanger of the cumene column.

Specifically, by connecting the PIPB out-put line 34 to one or more heatexchangers B selected among the heat exchanger B of the benzene column10 and heat exchanger B of the cumene column 20, the above-describedPIPB may be passed through any one or more heat exchangers selectedamong the heat exchanger of the benzene column and heat exchanger of thecumene column. Accordingly, the vapor heat source of PIPB can berecycled into the heat source of the benzene column 10 and/or cumenecolumn 20, thus increasing the energy efficiency.

Hereinafter, an example of the present application and a comparativeexample will be provided. The example below is provided merely to helpunderstanding of the present application, and it should not beunderstood as limiting the technical scope of the present application.

[Example 1]

Cumene was purified using an apparatus as shown in FIG. 5. The apparatusshown in FIG. 5 is identical to the apparatus shown in FIG. 2, but inFIG. 5, Q was specified for the description of the heat energy consumedin each of columns 10, 20 and 40.

Referring to FIG. 5, fresh benzene 41 and a stream 42 which wasdischarged from the alkylation reaction unit were introduced througheach of in-put lines 41 and 42 into the lights cut column 40.

Lights and water were removed through an upper out-put line 44, whereasa lower stream was introduced through a lower out-put line 46 into thebenzene column 10.

As for the benzene column 10, the lower stream 46 from the lights cutcolumn 40 was introduced through the in-put line 12 along with a stream12 discharged from the trans alkylation reaction unit. Also, benzene wasdischarged from the upper portion through the out-put line 14 to berecycled into the lights cut column 40, whereas a cumene stream wasdischarged from the lower portion through the out-put line 16 andintroduced into the cumene column 20.

In addition, in the cumene column 20, cumene was discharged from theupper portion through the out-put line 25, but it was passed through theheat exchanger B of the benzene column 10 for heat supply. The PIPBstream discharged from the lower portion through the out-put line 26 wasintroduced into the PIPB column 30. In addition, in the PIPB column 30,PIPB was discharged from the upper portion through the out-put line 34to be recycled into the trans alkylation unit, and heavies weredischarged from the lower portion through the out-put line 36 andcooled.

To carry out the purification process according to this example, adropping of the internal pressure P₁ of the benzene column 10 wasinduced. In this case, the internal pressure P₁ of the benzene column 10was reduced by a vacuum pump 15 installed at one end of the benzenecolumn 10 and maintained at about 35 kPa. The temperature T₁ at theupper portion and temperature T₂ at the lower portion of the benzenecolumn 10 were maintained at about 50° C. and about 150° C.,respectively, through a dropping of the internal pressure P₁. Also, thetemperature T₃ at the upper portion of the cumene column 20 wasmaintained at about 160° C. Here, each of the temperatures T₁ and T₃ atthe upper portions is the averaged temperature at the upper portion ofeach column, whereas the temperature T₂ at the lower portion is anaveraged temperature of the lower portion of a column. In addition, theheat energy Q₀ supplied to the lights cut column 40, heat energy Q₁supplied to the benzene column 10, heat energy Q₂ supplied to the cumenecolumn 20 and heat energy Q₃ discharged from the upper portion of thecumene column 20 were measured. The measurements are shown in Table 1below.

[Comparative Example]

Cumene was purified using an apparatus as shown in FIG. 4. The apparatusshown in FIG. 4 is identical to the apparatus shown in FIG. 1, but inFIG. 4, Q was specified for the description of the heat energy consumedin each of columns 1 and 2. The comparative example is a conventionalgeneral process, and description of the specific process well-known inthe art will be omitted.

Referring to FIG. 4, fresh benzene la, a stream 1 b discharged from analkylation reaction unit and a stream 1 c discharged from a transalkylation reaction unit were introduced to a benzene column 1respectively through each of in-put lines 1 a, 1 b and 1 c. Also,discharges of lights and water through an upper out-put line 1 d,benzene through a central out-put line if and a cumene stream through alower out-put line 1 e were carried out.

In addition, cumene was discharged through an out-put line 2 a at theupper portion of a cumene column 2 to be recovered, and a PIPB streamdischarged through an out-put line 2 b at the lower portion wasintroduced to a PIPB column 3. Also, PIPB was discharged through anout-put line 3 a at the upper portion of a PIPB column 3 to be recycledinto a trans alkylation reaction unit, and heavies were dischargedthrough an out-put line 3 d at the lower portion and cooled.

In the purification process as the above, the internal pressure P₁ ofthe benzene column 1 was maintained at about 310 kPa, and thetemperature T₁ at the upper portion and temperature T₂ at the lowerportion of the benzene column 1 were maintained at about 50° C. andabout 215° C., respectively. Also, the temperature T₃ at the upperportion of the cumene column 2 was maintained at about 160° C. Here,each of the temperatures T₁ and T₃ at upper portions is an averagedtemperature at the upper portion of each column, whereas the temperatureT₂ at the lower portion is an averaged temperature of the lower portionof a column. In addition, the heat energy Q₁ supplied to the benzenecolumn 1, heat energy Q₂ supplied to the cumene column 2 and heat energyQ₃ discharged from the upper portion of the cumene column 2 weremeasured. The measurements are shown in Table 1 below.

TABLE 1 <Results of heat energy evaluation> P1 Amount Note (kPa) T3-T2Q₀ Q₁ Q₂ Q₃ Q_(T) saved (ΔQ) Comparative 310 −55° C. —  8.4 5.2 6.1 13.6— Example Example  35   10° C. 0.95 6.94 7.6 6.1 9.39 4.21 P1: internalpressure of benzene column (kPa) Q₀: heat energy supplied to lights cutcolumn (Gcal/hr) Q₁: heat energy supplied to benzene column (Gcal/hr)Q₂: heat energy supplied to cumene column (Gcal/hr) Q₃: heat energy ofcumene discharged from cumene column (Gcal/hr) Q_(T): sum of heat energyactually used in purification process (Gcal/hr) T₃: temperature at upperportion of cumene column T₂: temperature at lower portion of benzenecolumn

As shown in Table 1 above, it can be seen that, when a dropping of thetemperature T₂ at the lower portion is induced and the vapor heat sourceQ₃ of cumene is supplemented as the heat source Q₁ of the benzene column10 through a dropping of internal pressure P₁ of the benzene column 10according to Example of the present application, heat energy of 4.21Gcal/hr can be saved (saved by about 31%).

In this case, the heat energy Q₁ supplied to the benzene column 10 is6.94 Gcal/hr, but the heat energy Q₃ of cumene at 6.1 Gcal/hr issupplied to the benzene column 10, and thus, the heat energy Q₁ Q₃actually used in the benzene column 10 is 0.84 Gcal/hr. The heat energyQ_(T) actually used in the purification process is 9.36 Gcal/hr in thecase of the example, indicating that significant amount of energy issaved as compared to 13.6 Gcal/hr in the case of the comparativeexample.

1.-7. (canceled)
 8. A method for purifying cumene, the method comprising: a light material removal process in which a stream from an alkylation reaction unit is introduced to a lights cut column to be removed of lights and water; a benzene separation process in which a stream from a transalkylation reaction unit and a stream discharged through a lower portion of the lights cut column are introduced to a benzene column to be separated into benzene and a cumene stream; a cumene separation process in which the cumene stream separated above is introduced to a cumene column to be separated into cumene and a polyisopropylbenzene stream; and a polyisopropylbenzene separation process in which the polyisopropylbenzene stream separated above is introduced to a polyisopropyl column to be separated into polyisopropylbenzene and heavy materials.
 9. The method of claim 8, wherein the light material removal process further includes introduction of benzene to a benzene input line which is installed in a front end portion.
 10. The method of claim 8, further comprising: a process of passing the cumene discharged at an upper portion of the cumene column through a heat exchanger of the benzene column.
 11. The method of claim 8, wherein a temperature at a lower portion of the benzene column is maintained in a range of 130° C. to 200° C.
 12. The method of claim 8, wherein a temperature at an upper portion of the cumene column is maintained in a range of 140° C. to 210° C.
 13. The method of claim 8, wherein the benzene column and cumene column are operated in a way so as to satisfy Mathematical Formula 1 below: T₃-T₂>10° C. [Mathematical Formula 1] (In the Mathematical Formula 1 above, T₂ is the temperature at a lower portion of the benzene column, and T₃ is the temperature at an upper portion of the cumene column).
 14. The method of claim 8, wherein an internal pressure of the benzene column is maintained in a range of 10 kPa to 230 kPa.
 15. The method of claim 8, further comprising: a process of passing the polyisopropylbenzene discharged at an upper portion of the polyisopropylbenzene column through one or more heat exchangers selected among a heat exchanger of the benzene column and a heat exchanger of the cumene column. 